On August 5, 2015, 3 million gallons of acid mine drainage was accidently released from the Gold King Mine spill, eventually reaching the San Juan River - the lifeblood of the Navajo Nation. Many Native American communities have subsistence livelihoods and strong cultural practices and spiritual beliefs that are deeply connected to the natural environment. As a result, environmental contamination from catastrophic mine spills severely impacts indigenous people to the core of their spiritual and physical livelihoods and there is potential for unique exposure pathways and greater health risks. Further complicating the situation is the lack of empirical short and long-term exposure data following mine spills, necessary for scientists to address these concerns. Building on established partnerships with the Navajo Nation, this project aims to measure the short- term exposure to lead and arsenic and evaluate the risk perceptions of Navajo communities dependent on the San Juan River in order to understand the potential long-term health risks from the Gold King Mine spill and develop mitigation strategies. Exposure and health effects of lead and arsenic are widely studied and clear guidelines for human biomonitoring levels are established such that individuals with high risks can be identified and treated before adverse health effects occur. The first aim is to determine levels of exposures in three Navajo Chapters downstream of spill within 9 months of the spill and prior to the growing season. The second aim is to assess temporal and spatial changes in sediment, agricultural soil, river and well water in the three Navajo Chapters within 12 months of the spill. The third aim is to determine the association between Navajo community members' perception of health risks and measured health risks from the Gold King Mine spill within the 9-month period after the spill. This application is time-sensitive because it is essential to obtain baseline short-term exposure measurements prior to spring runoff which is likely to re-mobilize river sediment and prior to the start of the Navajo growing season. Additionally, risk perception is most elevated, dynamic, and diverse shortly after an incident and recall bias should be minimized. The unpredictable timing of a mine spill of this magnitude increases the importance of a timely response for the collection of samples to evaluate potential harm to human health from environmental exposures. The results of this investigation will be used in the future to develop a community-based intervention, designed to a) prevent potentially harmful exposures based on actual measured risk, and/or b) communicate the actual long-term risks from the Gold King mine spill, effectively. While this specific incident may have been one of the largest acid mine spills in recent history, the Department of Interior has estimated more than 500,000 abandoned mines throughout the United States, and the potential for ongoing acid mine leaks or large-scale spills to impact many communities and eco-systems is high. Empirical data collected from this study could also be used to improve risk assessment and communication in the unfortunate event of future mine spill disasters affecting other communities.